Method of fabricating a composite superconductor

ABSTRACT

A plurality of rods are assembled in a predetermined configuration to form a core which is surrounded by a molten matrix metal within a heated crucible. The temperature of the thusly charged crucible&#39;&#39;s upper portion is maintained above the matrix metal&#39;&#39;s melting point. In this respect, as the heat is applied to the top of the melt, the crucible is maintained in a hot environment while the bottom of the crucible is centrally chilled. In this manner the charge is solidified from the bottom toward the top so that the solidification progresses upwardly and outwardly in a conical pattern. After the controlled solidification is completed the casting is separated from the crucible to form a cored extrusion billet. In one embodiment the rods are separated from the casting and the resulting open holes are filled with superconductive material to form a composite superconductor extrusion billet. In another embodiment the rods themselves are made of a superconductive material so as to eliminate the step of separating the rods from the casting.

United States Patent [191 Raymond et al.

[ 1 Mar. 12, 1974 METHOD OF FABRICATING A COMPOSITE SUPERCONDUCTOR 1Inventors 12m flemeRay n 8.20s...

[22] Filed: Sept. 24, 1971 [21] Appl. No.: 183,544

Related U.S. Application Data [63] Continuation of Ser. No. 47,390, June18, 1970.

[52] U.S. Cl 29/599, 29/527.6, 164/4, 164/76, 164/103, 164/122, 174/126CP,

[51] Int. Cl H0lv 11/00 [58] Field of Search 164/76, 98, 100, 103, 105,164/108,1l0,112, 4,122, 60, 132; 174/126 CP, DIG. 6; 335/216; 29/194,599, 527.5, 527.6

OTHER PUBLICATIONS A. Hare et al., A Method of Casting Radiator-TypeFuel Elements for a Nuclear Reactor Transactions of the AmericanFoundrymens Society, Vol. 66, pp. 210-212, 1958.

Primary ExaminerCharles W. Lanham Assistant ExaminerD. C. Reiley, III

Attorney, Agent, or Firm-Griffin, Branigan & Kindness [57] ABSTRACT Aplurality of rods are assembled in a predetermined configuration to forma core which is surrounded by a molten matrix metal within a heatedcrucible. The temperature of the thusly charged crucibles upper portionis maintained above the matrix metals melting point. In this respect, asthe heat is applied to the top of the melt, the crucible is maintainedin a hot environment while the bottom of the crucible is centrallychilled. In this manner the charge is solidified from the bottom towardthe top so that the solidification progresses upwardly and outwardly ina conical pattern. After the controlled solidification is completed thecasting is separated from the crucible to form a cored extrusion billet.In one embodiment the rods are separated from the casting and theresulting open holes are filled with superconductive material to form acomposite superconductor extrusion billet. In another embodiment therods themselves are made of a superconductive material so as toeliminate the step of separating the rods from the casting.

4 Claims, 5 Drawing Figures FIG. 2

PAIENTEU m I 21974 FIG. 3

PATENTEMR'Z'B" 3.795.978

SHEET 2 OF 2 HEAT 1 FURNACE HEAT TEMP CONTROL 48 CHILL WATER 58\ FIG. 5

METHOD OF FABRICATING A COMPOSITE SUPERCONDUCTOR This is a division, ofapplication Ser. No. 47,390, filed June 18, 1970.

BACKGROUND OF THE INVENTION The present invention relates to a methodand apparatus for producing pattern-cored extrusion billets forcomposite superconductors; and to the production of particularly highquality superconductor wire.

Composite superconducting wire is comprised of strands ofsuperconductive material imbeded in a matrix of a metal such as copperand is frequently extruded from a billet. One form of superconductivewire includes upward to 1,000 filaments of superconductor alloydistributed in an array in a normal metal matrix such as copper. Thesefilaments should be continuous from one end of the wire or strip to theother and separated from one another over their entire length by thematrix material. Such composite structures are currently fabricated bytechniques involving extrusion of composite billets that aresubsequently swaged, drawn, or rolled into superconductive wire, rod orstrips which form the final product. Each billet used in the extrusionprocess is conventionally in the form of a right circular cylindricalmatrix of normal metal such as copper in which rods of a superconductingmaterial are arranged with their long axes parallel to the longitudinalaxis of the matrix cylinder. In this respect, it is customary to formsuch a billet by drilling holes in a copper slug'and then loading theholes with a superconductive material.

Alternatively, a plurality of wafers of the matrix metal have holesdrilled therein in a predetermined pattern. The wafers are then stackedup so that their holes are aligned for receipt of superconductive rods.This wafer-rod structure is then encased to form an extrusion billet.Still another method of forming such billets is to form apattern-arranged bundle of rods comprised of the matrix material andsuperconductive materials. This pattern arranged bundle of rods is thenencased to form either an extrusion billet or a smaller bundle that canbe swaged or drawn into a final product without employing the extrusionstep. A method of this type is described in U.S. Pat. Nos. 3,465,429 and3,465,430 to Barber et al.

All of the above methods of producing composite superconductor materialshave certain drawbacks. For example, there is considerable waste andexpense involved in drilling holes in the matrix metal; and it is alsoexpensive to properly encase the matrix and rods. Also, particularly inconnection with the wafer-rod structure, there is a tendency for thesuperconductive rods to break while they are being reduced to finalform. Similarly, where it is necessary to encase the billet elements,the casing must be removed after extrusion or it frequently causesundesirable burrs or jagged protrusions on the finished wire. Hence,objects of this invention are to provide not only a more economical andreliable method and apparatus for producing superconductive wire, but toprovide a superconductive wire which itself is a considerably higherquality than that obtained by prior art methods.

An intermediate object of the invention is to provide a superconductorextrusion billet that is substantially defect free. In this regard it isa principle of the invention to form such a billet by means of a uniquecasting technique. Barbet et al have suggested that extrusion billetscan be cast, but such techniques have not heretofore proven practical.One reason for this is the generally accepted belief that extremelyexpensive and sophisticated casting equipment would be necessary to makedefect free castings of the required geometry and size because of thelarge shrinkage tendencies and other defect producing mechanismsencountered during solidification of normal matrix metals.

In accordance with principles of the invention a cored billet matrix isformed in a manner similar to that sometimes used in connection withfuel elements for nuclear reactors. One such technique is described inan article by A. W. Hare and R. F. Dickerson appearing at p. 210 etseq., Vol 66 of the Transactions of American Foundrymens Society (1958).In this regard a plurality of rods are assembled in a predeterminedconfiguration to form a core which is surrounded by a controlled purityand composition molten matrix metal within a heated crucible. The top ofthe crucible and its charge are maintained above the matrix metalsmelting point; and, at the same time, a chill block is brought intocontact with the bottom center of the crucible while the sides of thecrucible are maintained in a hot environment. In this manner, the chargesolidifies from the bottom up and the center out so that it solidifiesin the pattern of an upwardly progressing cone. in this mannershrinkage, porosity and other defects are eliminated so that theresulting matrix metal is nonporous and uniform throughout. Moreover,the cast billet is formed without sophisticated and complex zonerefining equipment, vibrational casting apparatus, centrifugal castingdevices or the like. Consequently, the method of the invention isrelatively inexpensive.

A major advantage of the invention is the provision of a coredsuperconductor billet having a unitary matrix metal structure. In thisregard, where a plurality of matrix metal rods are assembled in acontainer there is considerable difficulty in bonding the similar-metalrods together. Some writers hold that it is not necessary to obtaincomplete bonding between the matrix metal elements, but we have foundthat complete bonding is quite important; and one of the reasons ourmethod results in a superior product is that the unitary matrix metalportion of our extrusion billet has no unbonded portions as will now bebriefly discussed.

When pattern arranged bundles of matrix metal rods and superconductorrods are placed in a container and co-reduced as in the method of Barberet al, the ductile but abrasive superconductor rods are almostinstantaneously bonded to their adjacent rods of normal matrix metal.Contiguous matrix metal rods, on the other hand, shift, slide, andreadjust under the stresses of coreduction. They then transmit unevenstresses to the ductile superconductor filaments so that the resultingfilaments in the composite billet do not have uniform cross-sectionsthroughout their lengths. Moreover, if the rods of normal metal are notsubstantially absolutely clean they are even less adequately bonded andthe resulting filaments are even less uniform. This, in turn, places arestriction upon the critical current density of the superconductor wirethat is drawn or otherwise formed from the composite billet. Theproducts resulting from the method of the instant invention, on theother hand, have uniform superconductor filaments whereupon they exhibitsubstantially higher useful critical current densities thancorresponding composite superconductors made by the above describedtechniques of the prior art.

One prior art technique for obtaining better bonding between the matrixmetal elements of a patternedqod billet has been to co-reduce the.billet at a relatively high temperature. Such high temperatures,however, cause the normal metal surfaces to react with surroundingactive gases to severly reduce the bonding characteristics of the normalmetal elements and thus degrade the quality of the product. Hence, whenthis technique has been employed it has been necessary to initallycreduce such composite structures in a vacuum or an inert-gasatmosphere. This, however, is a cumbersome and expensive procedure whichis not required when the method of the invention is employed.

It is often desirable to use long lengths of composite superconductorwire rather than two or more shorter pieces; and, longer pieces of suchcomposite wire are more susceptible to undesirably low critical currentdensities because there is a greater probability that the longer wirewill have a filament defect somewhere along its length. Hence, it isanother object of this invention to provide a method of making longlengths of composite superconductor wire having high critical currentdensity ratings. In this regard, it has become conventional practice totwist composite superconductor material in order to increase its usefulcritical current density in magnet applications. When compositesuperconducting materials are thusly twisted, however, normal metalbonding defects'are magnified and thus degrade the full benefit of thetwisting step. One of the advantages of the instant invention,therefore, lies in the ability of its resulting wire to be twisted so asnot to destroy the filament integrity and thus obtain the full benefitsof the critical current density increases due to the twist.

Another object of the invention is to provide a method of easily,accurately, and economically controlling theresistivity ratio ofcomposite superconductive wire; and in accordance with the principles ofthe invention dealing with this particular object, an alloying orcontaminant material is added to the molten matrix metal in an amountcorresponding to a predetermined resistivity ratio of the correspondingsuperconductor.

And finally, in accordance with further aspects of the invention, afterthe casting has been solidified as described above the cored casting isseparated from the crucible so that the rods can be removed if desired.In this event the resulting'holes can be filled with a superconductivematerial to form an extrusion billet which is drawn or otherwisesuitably reduced to form superconductive wire, rod, or strip. In thismanner the resulting product not only has operating superconductingcharacteristics that are far superior to those produced by prior artmethods, but the wire is free of burrs or jagged protrusions resultingfrom outer containers such as those'described in U. S. Pat. No.3,465,430. Hence the smooth surface obtained by this invention is easierto both fabricate and insulate.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects,features, and advantages of this invention will be apparent by thefollowing more particular description of preferred embodiments thereofas illustrated in the accompanying drawings wherein the same referencenumerals refer to the same parts throughout the various views. Thedrawings are not necessarily intended to be to scale, but rather arepresented so as to illustrate the principles of the invention in clearform.

In the drawings: FIG. 1 is an end view of a billet core used in anembodiment of the inventions method;

FIG. 2 is a sectional, view of the FIG. 1 billet core taken along thelines 2-2 of FIG. 1.

FIG. 3 is a schematic view of a portion of a furnace and crucibleadapted to practice a preferred embodiment of the inventions method;

FIG. 4 is a schematic illustration of the manner in which a billetmatrix is solidified during a directionally controlled freezing step ofthe methods preferred embodiment; and, 1

FIG. 5 is a schematic illustration of apparatus for controlling thesolidification of the billet matrix illustrated in FIG. 4.

DETAILED DESCRIPTION In the embodiment of the core array illustrated inFIGS. 1 and 2, a retainer plate is affixed to both a core support rod 12and a lower pattern plate 14. These elements are made of a high puritygraphite.

The lower pattern plate 14 and a corresponding upper pattern plate 16have holes 18 drilled therein to accommodate the ends of a plurality ofrods 20 preferably hollow quartz which have at least one end sealed asat 22 to prevent the escape of air and the entrance of copper during animmersion step to be described shortly.

The core array of FIG. 1 is assembled by screwing the graphite coresupport rod 12 into the lower rod retainer plate 10, sliding the lowerpattern plate 14 down the core support rod, and sliding the upperpattern plate 16 into its proper position on the core support rod. Boththe upper and lower pattern plates are then locked in position withsmall tungsten or graphite pins such as 26 and 28. Next, a suitablenumber of quartz tubes 20 are loaded in the partially assembled core byinserting them, closed end 22 up (to the right in FIG. 2) through theholes 18 in the top pattern plate 16 so that they'terminate incorresponding holes in the bottom pattern plate 14. Subsequent tocompletely installing the appropriate rod pattern, the top retainerplate 24 is slid down the core support rod 12 and securely pinned asdescribed above.

After the core array of FIG. 1 is constructed as described above, it isplaced in a furnace to be heated. At the same time, a crucible 30 (FIG.3) is placed on a somewhat donut-shaped stool 32 in a furnace 34. Inthis regard, the inside walls of the crucible are slightly tapered at arate of about inch per foot so that the crucibles inside diameter issmaller at its bottom end than its top which is covered by an insulatedplug 35. This graphite plug 35 is machined to both fit the top of thecrucible and accommodate a tube 36 for delivering inert gas to thecrucibles interior if desired.

The furnace has one or more primary heat inlets such as 38; one or moresecondary heat inlets such as 40; and a hole 42 in the bottom thereof toaccommodate a chill-block 44 which may be raised upwardly through thestool 32 to rest against the bottom of the crucible 30. A temperaturesensing element 46 enters the top of the crucible and passes along itsside to sense the temperature of the crucible at various points alongits length. A second temperature sensing element 48 extends up to thecrucible's bottom adjacent to the chillblock 44; and both of thetemperature sensing elements are connected to a temperatureindicator-controller 50 (see also FIG. 5).

The temperature indicator controller 50 provides outputs on lines 52 and54 to control primary and secndary heaters 56 and 58 respectively whichprovide heat to the primary and secondary heat inputs 38 and 40 to thefurnace as shown shown in FIG. 5. Similarly, the temperature control 50provides an output on line 58 for controlling a chill water supply 60which delivers chill water through conduit 62 to a chill water recess 64in the furnaces chillblock 44. The heaters and chill water supply canalso be controlled manually.

In practicing a preferred embodiment of the inventions method a chargeof high purity oxygen-free, highconductivity (OFI-IC) copper is placedin the crucible 30 as illustrated by dotted line 65 in FIG. 3. In thisregard, the crucible 30 is preferably 'of a high purity graphite inorder to minimize melt contamination from this source. This isparticularly important where the inventions method is used to producesuperconductive wire having a high resistivity ratio. That is, the ratioof its resistance at room temperature to its resistance at thesuperconductive temperature such as 4.2 K, for example. Typicallydesired resistivity ratios are about 150-200, but this ratio dropsrapidly as impurities are introduced into the copper. To this end, theuse of graphite is significant because it does not combine with copper,but the crucible can also be made out of other materials which would notcontaminate the copper. Similarly, matrix materials other than coppercan also be used; and, in those cases where it is desired to provide asuperconductor having a low resistivity ratio the copper or other matrixcan be intentionally alloyed. For example, as little as 7 percent nickledrops the resulting structures resistivity ratio to about 5:1. In thisregard, it has been found that the method of the invention is admirablysuited for both accurately and inexpensively controlling the resistivityratio of composite superconductive wire. For any given combination ofnormal metal and superconductor metal the composite wires resistivityratio can be controlled to within an accuracy that has not beenpreviously obtainable in commerically available composite wire.

After the charge has been melted and superheated, it fills the crucibleto about the level of line 66 in FIG. 3. At this point, the preheatedcore assembly is slowly lowered into the'melt so as to be covered bymolten copper. The primary heater is then turned off and the melt issubjected to a controlled unidirectional freezing step which will now bedescribed.

The temperature controller 50 is adapted to direct chill water fromsource 60 through conduit 62 to the chill-water cavity 64 of thechill-block 44. At the same time, heat from source 58 is directedthrough secondary heating conduits 40 toward the upper portion of thecrucible so that the top of the melt is maintained above the matrixmetal s melting point l,083 C centrigrade in the case of OFI-IC copper;and the crucible is kept in the furnace so that its sides, although notfurther specifically heated, are maintained in a hot environment. Inthis manner, the matrix gradually solidifies from the bottom up andinside out in a cone-like fashion so as to eliminate the casting defectsgenerally associated with uncontrolled solidification. For example,

with the controlled solidification step a shrinkage cavity does not formin the center of the billet as occurs if the melt solidifies from theoutside in.

In the above regard, it has been found that by simultaneouslycontrolling the chilling of the crucible 5 lower portion and heating itsupper portion during the solidification process a pyramid or cone typesolidification pattern results. That is, as illustrated in FIG. 4, themelt 68 solidifies first at its bottom center and then at its outeredges in the manner of an upwardly progressing pyramid or cone placed ontop of the previously solidified matrix below. For example, dotted-line70 might represent the extent of solidification at a first point intime; dotted line 72 might represent the extent of solidification at asubsequent point in time; and dotted-line 74 might represent the extentof solidification at a still later point in time. It is thissolidification cone pattern of progressive solidification that providesa casting that is substantially free of undesired voids or conventionalcasting defects.

After the casting is sufficiently cooled it is extracted from thecrucible with the core array cast inside. The portions of the castingcontaining the pattern and retainer plates are then cut off and, ifdesired, the outer surface of the casting is turned to the desireddimensions. In this regard, however, one of the advantages of theinvention is that only a small portion of the originally cast matrixmaterial is wasted. For example, the above described steps of turningand removing the end and retainer plates involves removing only about 5percent of the matrix material which, because of its high purity can bereused. Note, in this regard, that if holes are drilled in either aunitary structure or individual wafers it is quite difficult to maintainthe purity of the thusly removed material, whereupon it is notsatisfactory for subsequent use as a superconductive matrix.

If desired the quartz rods are next removed from the casting by aleaching process in which the quartz is dissolved under the action ofmolten sodium hydroxide. The hot billet is then water-quenched to ensureremoval of any undisolved quartz and to minimize oxidation of the billetsurface. Alternatively, the quartz rods can be removed by leaching inhydrofluoric acid solution or by mechanical means. After this the matrixcasting is cleaned by brushing, leaching, and washing in suitablereagents to provide clean active surfaces. The matrix holes are thenfilled with rods of superconductive elements or alloys such as niobium,or some appropriate superconducting alloy. For example, satisfactoryresults can be obtained by using a niobiumtitanium alloy having up to 70percent titanium (titanium 30 weight percent niobium); and in apreferred embodiment the composite billet consisted of titanium 45weight percent niobium rods embedded in an OFHC copper matrix. Whicheverthe case the composite billet is then extruded, swaged, drawn or in someother way fabricated into composite superconductive wire, rod or strip.

It will be appreciated by those skilled in the art that the abovedescribed method and apparatus for producing a uniform matrix alsoprovides a uniform, superior quality superconductive wire. In thisregard, not only is such wire more uniform, but there are far lessincidents of filament damage than in wires made by prior art processes.Consequently, the resulting wire can be drawn into much longer lengthswithout suffering a reduction in useful critical current density. Forexample,

a comparison was made between composite wire made by a conventionalmethod and composite wire of the same diameter and composition, but madeby the above described method. The maximum length of high qualitycomposite 0.050 inch diameter wire made by the conventional method was4,000 feet, while high quality 0.050 inch wire of the instant inventionwas drawn to 40,000 feet and it could have been longer if desired.

Also, the surface of the resulting wire is free of burrs as opposed tothat of prior art processes because the compositeextrusion billet is notsegmented and thus it is not necessary that the billet be placed in acontainer prior to drawing. Hence, there are no undesirable protrusionsor burrs in the final wire so that it is considerably easier toinsulate. it should also be noted that when superconductive wires madein accordance with the invention are placed in structures such assuperconductive magnets, they result in a magnet that is much easier toenergize because it is both easier to insulate in a short-free manner;and capable of obtaining a higher flux density because of its filamentintegrity.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention. For example, it will be appreciated that the above describedcentral graphite supporting rod could be a supporting circumferentialsleeve or longitudinal straps, the quartz tubes could be drilled out;and the inventions method can also be applied to continuous casting.Also, other materials can be used than those specifically described. Forexample, rods of stainless steel or other suitable metals can be coatedwith Al Ti 0 or other refractory compounds, and such structures can beused in placeof the quartz rods described above; and, if the rods aretapered, they can be removed mechanically.

The configuration of the crucible mold, core components and billet canalso be changed markedly without departing from the spirit of theinvention. For example, 7

square or hexagonal cross sectioned billets can be produced; and optimumpacking factors may make it desirable to use core rods having hexagonal,triangular or other geometrical shapes.

The quartz rods can also be replaced with superconductor rods whosesurfaces have been treated with niobium, molybdenum, tungsten, or thelike so as not to combine with the matrix metal and/or form compoundsdetrimental to the fabrication and useful current density of thesuperconducting end product.

In this regard the invention can be practiced by placing core rodscomposed of a superconducting material directly in the core assembly toproduce a finished extrusion billet as the cast product rather than acored extrusion matrix that must subsequently be loaded with asuperconductive material to form the finished composite extrusionbillet. For example, Ti-Nb core rods can be directly cast in an aluminummatrix. Also, instead of inserting the core assembly into the moltenmatrix metal, the core can be fixed in the crucible and the moltenmatrix metal introduced from an outside source; and, in this respect, itwill be appreciated that other matrix metals such as lead and tin canalso be used. Hence, it will be apparent that the invention can bepracticed in many manners other than those which have been specificallydescribed above. I

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

We claim: 1. A method of making a composite superconductor productcomprising the steps of:

creating a melt of matrix metal in a form; locating in said melt ofmatrix metal an array of preheated superconductive rods such that themelt envelopes the array of rods; sensing the temperature of said format predetermined points running from the bottom to the top thereof;controlling the solidification of said melt of matrix metal from thebottom of said form to the top thereof in accordance with said sensedtemperature in a manner such that said solidification progressesupwardly in the pattern of a cone so as to eliminate undesired voids andcasting defects, and obtain a nonporous uniform billet; separating thesolidified matrix and said array from said form to provide a cast billetsuitable for manufacturing into a composite superconductor product;working said cast billet to reduce its cross section;

and, fabricating said worked cast billet to form a compositesuperconductor product. 2. A method of making a composite superconductorproduct comprising the steps of:

creating a melt of matrix metal in a form; locating an array ofpreheated hole-shaping removable rods in said melt of matrix metal suchthat the melt envelopes the array of rods; sensing the temperature ofsaid form at predetermined points running from the bottom to the topthereof; controlling the solidification of said melt of matrix metalfrom the bottom of said form to the top thereof in accordance with saidsensed temperature in a manner such that said solidification progressesupwardly in the pattern of a cone so as to eliminate undesired voids andcasting defects, and obtain a nonporous uniform billet; separating thesolidified matrix and said array from said form to provide a cast billetsuitable for manufacturing into a composite superconductor product;separating said array of rods from said solidified matrix and array ofrods subsequent to the separation of said solidified matrix and saidarray of rods from said form to thereby leave open holes in said castbillet; filling said open holes in said cast billet with asuperconductive material; working said cast billet to reduce its crosssection;

and, fabricating said worked cast billet to form a compositesuperconductor product. 3. A method of making a composite superconductorproduct comprising the steps of:

constructing an array of hole-shaping removable parallel rods in a frameso that said rods are arranged in a pattern about a central longitudinalaxis; preheating said array of parallel rods and said frame;

locating a matrix metal in a crucible and heating said matrix metal insaid crucible to a molten state;

inserting said preheated array of parallel rods and said frame in saidmolten metal matrix in said crucible;

sensing the temperature of said crucible at predetermined points fromthe bottom to the top thereof;

solidifying said molten matrix metal from the bottom of said crucibletoward the top thereof in accordance with the sensed temperature in amanner such that solidification progresses upwardly in the pattern of acone by cooling the melt of said molten matrix metal at the bottomwhile: i maintaining said crucible in a hot environment above themelting point of said molten matrix elongated composite superconductorelement.

gz gg UNITED STATES PATENT vOFFICE CERTIFICATE OF CORRECTION Patent No.3,795,97 Dated March 12, 197W Inventor(s) JanW. Raymond and Clay N.Whetstone It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Add to the heading of the Patent as section (73) 2 Assignee:Cryomagnetics Corporation, Denver, Colorado Signed and sealed this 22ndday of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHAI: ,L DANN Attesting Officer Conunissionerof Patents Fgiggo UNITED STATES PATENT .oFFIC -j CERTIFICATE OFCORRECTION Patent No 3,795,97 I Dated March 12, 197

Inventor(s) Jan'W. Raymond and Clay N. Whetstohe It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as, shown below:

Add to the heading of the Patent 7 as section. (73) Assignees Cryomag'netics Corporation, Denver, Colorado Signed andse'aled this 22nd dayof October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHAILZL, DANN Attesting OfficerCommissioner-of Patents

1. A method of making a composite superconductor product comprising thesteps of: creating a melt of matrix metal in a form; locating in saidmelt of matrix metal an array of preheated superconductive rods suchthat the melt envelopes the array of rods; sensing the temperature ofsaid form at predetermined points running from the bottom to the topthereof; controlling the solidification of said melt of matrix metalfrom the bottom of said form to the top thereof in accordance with saidsensed temperature in a manner such that said solidification progressesupwardly in the pattern of a cone so as to eliminate undesired voids andcasting defects, and obtain a nonporous uniform billet; separating thesolidified matrix and said array from said form to provide a cast billetsuitable for manufacturing into a composite superconductor product;working said cast billet to reduce its cross section; and, fabricatingsaid worked cast billet to form a composite superconductor product.
 2. Amethod of making a composite superconductor product comprising the Stepsof: creating a melt of matrix metal in a form; locating an array ofpreheated hole-shaping removable rods in said melt of matrix metal suchthat the melt envelopes the array of rods; sensing the temperature ofsaid form at predetermined points running from the bottom to the topthereof; controlling the solidification of said melt of matrix metalfrom the bottom of said form to the top thereof in accordance with saidsensed temperature in a manner such that said solidification progressesupwardly in the pattern of a cone so as to eliminate undesired voids andcasting defects, and obtain a nonporous uniform billet; separating thesolidified matrix and said array from said form to provide a cast billetsuitable for manufacturing into a composite superconductor product;separating said array of rods from said solidified matrix and array ofrods subsequent to the separation of said solidified matrix and saidarray of rods from said form to thereby leave open holes in said castbillet; filling said open holes in said cast billet with asuperconductive material; working said cast billet to reduce its crosssection; and, fabricating said worked cast billet to form a compositesuperconductor product.
 3. A method of making a composite superconductorproduct comprising the steps of: constructing an array of hole-shapingremovable parallel rods in a frame so that said rods are arranged in apattern about a central longitudinal axis; preheating said array ofparallel rods and said frame; locating a matrix metal in a crucible andheating said matrix metal in said crucible to a molten state; insertingsaid preheated array of parallel rods and said frame in said moltenmetal matrix in said crucible; sensing the temperature of said crucibleat predetermined points from the bottom to the top thereof; solidifyingsaid molten matrix metal from the bottom of said crucible toward the topthereof in accordance with the sensed temperature in a manner such thatsolidification progresses upwardly in the pattern of a cone by coolingthe melt of said molten matrix metal at the bottom while: i maintainingsaid crucible in a hot environment above the melting point of saidmolten matrix metal; and, ii heating said crucible at the top tomaintain the temperature thereof above the melting point of said moltenmatrix metal until the top of said melt solidifies; separating thethusly formed billet from said crucible; separating said parallel rodarray from said thusly formed billet to leave open holes in said billet;and, filling said open holes with a superconductive material to form acomposite superconductor product.
 4. The method of claim 3 including thestep of: working said composite product to form a slender elongatedcomposite superconductor element.